Do charges in electric circuit move only if the circuit closed?

Thread Starter

Alchemy One

Joined Oct 5, 2019
205
This has really been bugging me to say the least.
The fact that a circuit has to be closed for charged to move, do work that is, transfer energy to the load etc.
However charges do move in open circuit, does it not?
Antenna is an open circuit to my knowledge.
Howabout an obvious observation. When you hook up two wires one in each terminal of a battery, isn't there voltage difference at the end of the wires even if the wires are in opposite direction away from each other?

Tree does not fall in the forest unless someone hears it.

Can someone explain this in such a way that it actually makes sense. Lets keep it simple and use electrons moving in conductors. Not ions, molecules etc.
 
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crutschow

Joined Mar 14, 2008
29,755
There is always some stray capacitance from any wire to ground or to any other wire.
So when there is a voltage change or change in the wire length or position, then the electrons will move to charge/discharge that capacitance.
But there is no steady movement (other than thermal vibration) of the electrons unless there is a closed circuit.

And as Yaakov noted, an antenna is not an open circuit, it has an AC radiation impedance to free space.
For example, the radiation impedance for a half-wave dipole antenna in free space is 73 Ω.
 

Papabravo

Joined Feb 24, 2006
18,400
In the simplest of terms there are two kinds of charge motion:
  1. Random drift motion
  2. Motion due to a potential difference
Now, at any temperature above absolute zero (≈-273 °C), particles will move in random directions with random velocities due to thermal energy in the surroundings. The randomness of the motion limits any practical applications of that random motion due to temperature.

When there is a potential difference, and a complete circuit, then potential energy can be converted into kinetic energy (energy of motion) and work will be done.
 

nsaspook

Joined Aug 27, 2009
9,704
and of course the kinetic energy of the charged particles (electrons) is wasted as heat in the antenna. The transfer of electrical energy in the antenna circuit is due to the fields surrounding it from transmission line field energy.
 

nsaspook

Joined Aug 27, 2009
9,704
So where does the electron kinetic energy go if the antenna is made from a superconductor?
There would be no KE losses in a perfect electrical conductor but a superconductor is not a perfect electrical conductor. For a practical superconductor the RF losses depend on several QM effects seen as AC impedance but the end result is much higher Q for traditional superconductor RF materials.
https://www.sciencedirect.com/science/article/pii/S1110016812000178

It would reduce resistive losses and at least in theory, increase antenna efficiency in electrically short antennas where resistive value losses are a sizable fraction of the total radiation resistance.

sca.pngpec.png
 
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Thread Starter

Alchemy One

Joined Oct 5, 2019
205
There are already two threads running on this topic. No point in starting a third.

https://forum.allaboutcircuits.com/threads/voltage-vs-current-which-occurs-first.184910/

I will post the link to the other one when I find it.
===================================
That is clearly about different subject. It is obvious just by reading the very link itself you have pasted.
Am I asking which occurs first, voltage or current?
I just don't see it in my post at all, nor should it be interepreted that way.
 

Thread Starter

Alchemy One

Joined Oct 5, 2019
205
In the simplest of terms there are two kinds of charge motion:
  1. Random drift motion
  2. Motion due to a potential difference
Now, at any temperature above absolute zero (≈-273 °C), particles will move in random directions with random velocities due to thermal energy in the surroundings. The randomness of the motion limits any practical applications of that random motion due to temperature.

When there is a potential difference, and a complete circuit, then potential energy can be converted into kinetic energy (energy of motion) and work will be done.
=================================
So what is the answer that directly relates to my question?
Where do you find [I, current, amps] in closed or open circuit?
If not in open circuit, then what moves in the antenna and when you simply hook up wires to a battery?
Did I just repeat myself? I seem to always do.
On extremely (rare occasion) I don't. Those are the moments. Too bad they don't happen often.
Sometime someone comes along and answers the question and makes my day. But I know never to get used it. And I won't.
( I am suppose to thank for whatever I get. Why? Because people are just trying to help. That is what I will be made to read and notice)
 

nsaspook

Joined Aug 27, 2009
9,704
This has really been bugging me to say the least.
The fact that a circuit has to be closed for charged to move, do work that is, transfer energy to the load etc.
However charges do move in open circuit, does it not?
Antenna is an open circuit to my knowledge.
Howabout an obvious observation. When you hook up two wires one in each terminal of a battery, isn't there voltage difference at the end of the wires even if the wires are in opposite direction away from each other?

Tree does not fall in the forest unless someone hears it.

Can someone explain this in such a way that it actually makes sense. Lets keep it simple and use electrons moving in conductors. Not ions, molecules etc.
The problem you have is with the limitations of circuit theory (that doesn't try to explain energy transfer), not antenna theory or electromagnetics in general. You can't use the simplistic model of circuit theory to explain antenna (EM) theory but you can use EM theory to explain and solve circuit theory domain problems because it's not based on assumptions that make for easy calculation of basic circuits where energy transfer mechanisms are not included in the actual theory but are assumed (usually by using electrons or charges) by the people using circuit theory.
 

Papabravo

Joined Feb 24, 2006
18,400
=================================
So what is the answer that directly relates to my question?
Where do you find [I, current, amps] in closed or open circuit?
If not in open circuit, then what moves in the antenna and when you simply hook up wires to a battery?
Did I just repeat myself? I seem to always do.
On extremely (rare occasion) I don't. Those are the moments. Too bad they don't happen often.
Sometime someone comes along and answers the question and makes my day. But I know never to get used it. And I won't.
( I am suppose to thank for whatever I get. Why? Because people are just trying to help. That is what I will be made to read and notice)
If the instrument has the sensitivity, you can measure even very small currents in an open circuit. In an antenna you can measure AC currents if the device has the appropriate bandwidth. What you can measure has absolutely nothing to do with what you can make use of.
 

Thread Starter

Alchemy One

Joined Oct 5, 2019
205
If the instrument has the sensitivity, you can measure even very small currents in an open circuit. In an antenna you can measure AC currents if the device has the appropriate bandwidth. What you can measure has absolutely nothing to do with what you can make use of.
============================
"What you can measure has absolutely nothing to do with what you can make use of".
You left me to assume that by "What" you mean current. Not good to assume things, it comes back and bites the person.
If my assumption is right, it makes usefulness a different subject.

Since the teaching is that for charges to move (i.e. current) you need a closed circuit, you have to close the circuit, a person does not want to be in a position to say current also move in open circuit.

I am left to conclude, having to read all the run arounds and reading between the lines and it actually looks like this ( I do not see other choice):

Charges do move in open circuit with a little more than just drifting about, but not much.
Open circuit with higher voltages, they move a little more and still not enough to amount to hardly anythying.
And even when extreme high voltages that have in place in everyday life, charges still won't move enough to amount to anything that can do work so to speak plus they have no place to go.
Yes in antenna they have no place to go to and that is why very little move indeed. Just enough to get the job done but not enough it will light up the smallest LED just being hooked up in one leg. But it might if there is enough field, there is no tellling, depending on the system.

Why is this?
It is because in open circuit it equates to applying energy to separate charges and removing them from the system. It will take profound energy to do so. It is what takes place in a particle accelerator. You are removing proton from hydrogen atom and you have to use tremendous means of keeping them separate from electrons and send them their merry way.

So what do they do with the left over electrons since the proton gets torn apart to smotherine, oblivion extinction?

I guess I ended up answering my own question in a way that it actually makes sense and is directed to the question itself.
Talk long enough to myself and the answer is revealed in a very direct clear simple manner. It happens 99% of the time.
 
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Ya’akov

Joined Jan 27, 2019
5,642
I don't understand what you think charge is and what you mean when you say "move" in relation to it.
I don't understand what you mean about the antenna.

I think it would be exceedingly helpful for you to define your terms:

  1. charge
  2. move
  3. electric
  4. circuit
  5. open circuit
  6. closed circuit

As it stands I don't think there is even an agreement on the meaning of the words in your question which would make an answer useless.
 

nsaspook

Joined Aug 27, 2009
9,704
============================
...
Why is this?
It is because in open circuit it equates to applying energy to separate charges and removing them from the system. It will take profound energy to do so. It is what takes place in a particle accelerator. You are removing proton from hydrogen atom and you have to use tremendous means of keeping them separate from electrons and send them their merry way.

So what do they do with the left over electrons since the proton gets torn apart to smotherine, oblivion extinction?
...
No, it doesn't take profound (if that means large) energy to seperate 'free' charges. 'Free' charges are usually easy to move because that is the definition of good conductance in a circuit conductor. Antennas (closed circuits for field energy) are profoundly simple (in action, not the scientific notation needed to describe and predict behaviour) devices in electromagnetics that exist naturally like the molecules in photosynthesis that capture EM energy (like a satellite dish, collecting energy from a large area and concentrating it at a small receiver site) in the visible range fo run chemical reactions. There's no need to overcome nuclear binding forces to have simple EM radiation and capture from charge separation.

For people like you who are interested in learning more I would highly suggest finding, reading and understanding this book.
https://www.barnesandnoble.com/w/the-fields-of-electronics-ralph-morrison/1112114935
A practical new approach that brings together circuit theory and field theory for the practicing engineer
To put it frankly, the traditional education of most engineers and scientists leaves them often unprepared to handle many of the practical problems they encounter. The Fields of Electronics: Understanding Electronics Using Basic Physics offers a highly original correction to this state of affairs.
Most engineers learn circuit theory and field theory separately. Electromagnetic field theory is an important part of basic physics, but because it is a very mathematical subject, the connection to everyday problems is not emphasized. Circuit theory, on the other hand, is by its nature very practical. However, circuit theory cannot describe the nature of a facility, the interconnection of many pieces of hardware, or the power grid that interfaces each piece of hardware.
The Fields of Electronics offers a unique approach that brings the physics and the circuit theory together into a seamless whole for today's practicing engineers. With a clear focus on the real-world problems confronting the practitioner in the field, the book thoroughly details the principles that apply to:
* Capacitors, inductors, resistors, and transformers
* Utility power and circuit concepts
* Grounding and shielding
* Radiation
* Analog and digital signals
* Facilities and sites
Written with very little mathematics, and requiring only some background in electronics, this book provides an eminently useful new way to understand the subject of electronics that will simplify the work of every novice, experienced engineer, and scientist.
 
Last edited:

sparky 1

Joined Nov 3, 2018
716
Because the question includes "only if" about charge movement in an electrical circuit it is necessary to go beyond
electronics 101 or so to see that an electric field inside the gap between capacitor plates can develop a field that increases or decreases for a time.
The battery can also experience an electro-chemical reaction when presented with the gap. If the video continues past 1:37 seconds then conservation of energy is maintained by definition. With animation it is easier to visualize an electric field but without a model it is more difficult to communicate the details.


Michael Faraday could visualize the field but had trouble getting others to see that. Often in history of electrical science details are expressed with drawings that have been proceeded by Mathematics.

 
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Thread Starter

Alchemy One

Joined Oct 5, 2019
205
Because the question includes "only if" about charge movement in an electrical circuit it is necessary to go beyond
electronics 101 or so to see that an electric field inside the gap between capacitor plates can develop a field that increases or decreases for a time.
The battery can also experience an electro-chemical reaction when presented with the gap. If the video continues past 1:37 seconds then conservation of energy is maintained by definition. With animation it is easier to visualize an electric field but without a model it is more difficult to communicate the details.


Michael Faraday could visualize the field but had trouble getting others to see that. Often in history of electrical science details are expressed with drawings that have been proceeded by Mathematics.

==================================
Take a 12 volt car battery and hook up a 2 feet wire and attach it to any of the terminals of the battery and stretch the wire away from the battery, meaning away from the other terminal and not towards it. What moves to the end of that wire? voltage, current, power, resistance, energy, virtual photons, nothing, something, anything or who knows what moves?
Just a simple direct question.
 

Ya’akov

Joined Jan 27, 2019
5,642
==================================
Take a 12 volt car battery and hook up a 2 feet wire and attach it to any of the terminals of the battery and stretch the wire away from the battery, meaning away from the other terminal and not towards it. What moves to the end of that wire? voltage, current, power, resistance, energy, virtual photons, nothing, something, anything or who knows what moves?
Just a simple direct question.
Nothing moves, why would it? The distance between the terminals is shorter than the distance to the end of th wires, why do you need the wires in your thought experiment?

if anything moves at all it will be because of capacitive coupling of the terminals since there is no DC connection. At 12V the capacitance is too high to allow such a circuit to exist so things just stay where they are.

Why do you think anything moves i your gedankenexperiment? What are you visualizing that leads you to believe something does? If charge moved, it would be detectable. Charge moving through a conductor causes a magnetic field to form while it is moving, you would be able to measure that, it’s not there.

@nsaspook tried to explain that circuit theory is akin to classical physics compared to relativistic physics. It is a very powerful, incredibly useful tool but it is an analogy to the underlying cause-and-effect change, an isomorphic model that breaks down in cases where you exceed the limits of it’s mapping to the real underlying cause.

You are extending your incomplete knowledge of the effectively mechanical model of circuits you have built up and trying to incorporate and even more incomplete knowledge of field effects into it. If you really want to understand this, I highly and sincerely recommend you watch the Electricity and Magnetism lectures of Walter Lewin. at MIT.

They are the lectures given to the Physics II class, and if the calculus is to much for your current level you can ignore it and still get an enormous amount of information about the topic. He spends time showing how to derive the formulas, but that is not essential to the lecture. If you watch and really try to grasp the material I think it well change your perspective. This question will be replaced by far more cogent and profound questions about the nature of electromagnetism.

https://youtube.com/playlist?list=PLyQSN7X0ro2314mKyUiOILaOC2hk6Pc3j
 
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